JP2017053696A - Laser type gas analysis device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser type gas analysis device the filter characteristic of which is not changed by a temperature change or the permissible tolerance of an electronic component, and with which it is possible to accurately detect a signal of a frequency twice the frequency of a modulation signal.SOLUTION: A laser type gas analysis device comprises: a laser beam source 10 for outputting a laser beam; a laser drive circuit 14 for sending a current in which a high-frequency modulation signal is superposed on a sweep signal to the laser beam source and thereby driving the laser source; a light detection unit 16 for receiving the laser beam of the laser beam source via a cell; a switched capacitor notch filter 22 for removing the fundamental frequency of the modulation signal from the output of the light detection unit; an extraction unit 18 for exercising synchronous detection on the output of the switched capacitor notch filter and thereby extracting a second higher harmonic signal of the modulation signal; and a signal analysis circuit 19 for analyzing the second higher harmonic signal extracted by the extraction unit and measuring a gas concentration.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a laser gas analyzer for measuring a gas concentration in a sample cell using a wavelength tunable semiconductor laser.

  In recent years, a laser type gas analyzer using a wavelength tunable laser has been disclosed as a method for measuring the concentration of a specific gas in a gas (Patent Document 1).

  FIG. 12 is a circuit configuration diagram of a conventional laser gas analyzer. This gas analyzer includes a sine wave generator 11, a sawtooth generator 12, an adder 13, a laser driving circuit 14, a laser light source 10, a sample cell 15, a photodiode 16, an active bandpass filter 17, a lock-in amplifier 18, A signal analysis circuit 19 is provided.

  The sawtooth generator 12 generates a sawtooth signal (corresponding to a sweep signal) that sweeps an arbitrary absorption wavelength band of the measurement target gas, and outputs the sawtooth signal to the adder 13. The sine wave generator 11 generates a modulation signal composed of a sine wave having a frequency f that is about 10 to 1000 times the sweep signal generated by the saw wave generator 12, and outputs the modulation signal to the adder 13.

  The adder 13 superimposes the modulation signal from the sine wave generator 11 on the sawtooth signal from the sawtooth wave generator 12, and flows the obtained signal as a drive current to the laser light source 10 made of a wavelength tunable semiconductor laser.

  The laser drive circuit 14 drives the laser light source 10 by flowing a drive current in which the modulation signal from the sine wave generator 11 is superimposed on the saw signal from the saw wave generator 12 to the laser light source 10.

  The laser light source 10 oscillates by the drive current from the laser drive circuit 14 and irradiates the sample cell 15 with the laser light. The laser light source 10 is a wavelength tunable semiconductor laser that oscillates in the absorption wavelength band of the gas to be measured and outputs laser light, such as a DFB-LD or DFB-QCL (quantum cascade laser). The measurement target gas is NH3, NO, NO2, SO2, HCL, H2O, CO, CO2, O2, or the like.

  The laser light is absorbed by the gas in the sample cell 15. At this time, a change in gas absorption occurs at a frequency 2f that is twice the frequency f of the modulation signal.

  The photodiode 16 receives the laser light that has passed through the sample cell 15. The active band pass filter 17 reduces the gain of the frequency f of the modulation signal in the signal from the photodiode 16. The lock-in amplifier 18 obtains a second harmonic component (hereinafter referred to as 2f spectrum) by synchronously detecting the output of the photodiode 16 at a frequency twice that of the modulation signal. The signal analysis circuit 19 calculates the gas concentration based on the second harmonic component from the lock-in amplifier 18.

JP 2001-235420 A

  However, the active bandpass filter 17 alone cannot completely remove the modulation signal of the frequency f having a high signal strength, the dynamic range of the signal of the frequency 2f having a low signal strength for signal analysis is lowered, and the signal of the frequency 2f is accurately obtained. It cannot be detected.

  FIG. 13 shows the frequency characteristics of an active bandpass filter of a conventional laser gas analyzer. Here, since the modulation frequency f is 9.8 kHz, 1 f is 9.8 kHz, and 2 f is 19.6 kHz. It can be seen that the 1f signal can reduce the gain only by a few dB.

  However, if an attempt is made to significantly reduce the 1f signal, the difference between the 1f and 2f is small, so the gain of the 2f signal decreases.

  In addition, the filter characteristics change due to temperature changes and electronic component tolerances, so that desired characteristics cannot be obtained, and the dynamic range of signal detection at the frequency 2f cannot be increased.

  An object of the present invention is to provide a laser-type gas analyzer that can accurately detect a signal having a frequency twice the frequency of a modulation signal without changing filter characteristics due to temperature changes or tolerances of electronic components.

  In order to solve the above-described problem, a laser gas analyzer according to the present invention provides a laser light source that outputs laser light, and a current in which a high-frequency modulation signal is superimposed on a sweep signal. A laser drive circuit for driving a light source, a light detection unit that receives laser light of the laser light source through a cell, a switched capacitor notch filter that removes a fundamental frequency of the modulation signal from an output from the light detection unit, Extracting the second harmonic signal of the modulation signal by synchronously detecting the output of the switched capacitor notch filter, and analyzing the second harmonic signal extracted by the extraction unit to measure the gas concentration A signal analysis circuit is provided.

  The laser gas analyzer includes a laser light source that outputs laser light, a laser drive circuit that drives the laser light source by causing a current in which a high-frequency modulation signal is superimposed on a sweep signal to flow to the laser light source, A light detection unit that receives laser light from a laser light source via a cell; a switched capacitor bandpass filter that passes a second harmonic signal of the modulation signal from an output from the light detection unit; and the switched capacitor bandpass filter An extraction unit that extracts the second harmonic signal of the modulation signal by synchronously detecting the output of the modulation signal, and a signal analysis circuit that analyzes the second harmonic signal extracted by the extraction unit and measures the gas concentration It is characterized by that.

  According to the present invention, since the switched capacitor notch filter or the switched capacitor bandpass filter is used, the filter characteristics do not change due to temperature change or electronic component tolerance, and a signal having a frequency twice the frequency of the modulation signal can be accurately obtained. Can be detected.

1 is a circuit configuration diagram of a laser type gas analyzer of Example 1. FIG. It is a figure which shows the frequency characteristic of the switched capacitor notch filter of the laser type gas analyzer of Example 1. FIG. It is a figure which shows the frequency characteristic of each filter of the laser type gas analyzer of Example 1. FIG. 2 is a circuit configuration diagram of an integrator using a switched capacitor of the laser gas analyzer of Example 1. FIG. FIG. 3 is a circuit configuration diagram of a first switched capacitor notch filter of the laser type gas analyzer of Example 1. 3 is a circuit configuration diagram of a second switched capacitor notch filter of the laser type gas analyzer of Example 1. FIG. It is a circuit block diagram of the secondary band pass filter used for the conventional laser type gas analyzer. It is a circuit block diagram of the twin T notch filter used for the conventional laser type gas analyzer. 6 is a circuit configuration diagram of a laser type gas analyzer of Example 2. FIG. It is a figure which shows the frequency characteristic of the switched capacitor band pass filter of the laser type gas analyzer of Example 2. FIG. FIG. 6 is a circuit configuration diagram of a switched capacitor bandpass filter of the laser type gas analyzer of Example 2. It is a circuit block diagram of the conventional laser type gas analyzer. It is a figure which shows the frequency characteristic of the active band pass filter of the conventional laser type gas analyzer.

  Embodiments of a laser gas analyzer according to the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a configuration diagram of a laser gas analyzer according to the first embodiment. 1 includes a sine wave generator 11, a sawtooth generator 12, an adder 13, a laser drive circuit 14, a laser light source 10, a sample cell 15, a photodiode 16, a preamplifier 20, and a first high pass. It has a filter (first HPF) 21, a switched capacitor notch filter 22, a first low-pass filter (first LPF) 23, a lock-in amplifier 18, a second high-pass filter (second HPF) 24, and a signal analysis circuit 19a.

  Since the sine wave generator 11, the sawtooth wave generator 12, the adder 13, the laser drive circuit 14, the laser light source 10, the sample cell 15, and the photodiode 16 are the same as those shown in FIG. Omitted.

  The photodiode 16 corresponds to the light detection unit of the present invention. The lock-in amplifier 18 corresponds to the extraction unit of the present invention.

  The preamplifier 20 amplifies the output received by the photodiode 16 to a predetermined voltage. The first HPF 21 is set to a frequency at which the cutoff frequency exceeds the frequency band of the sawtooth signal, and removes the frequency band of the sawtooth signal from the output from the preamplifier 20 as shown in the filter frequency characteristics of FIG.

  The switched capacitor notch filter 22 removes the fundamental frequency of the modulation signal from the output signal from the first HPF 21, and includes capacitors C1, C2, switches S1, S2, an operational amplifier OA, and an inverter INV as shown in FIG. It has an integrator with characteristics.

  The voltage VIN is input to one end of the switch S1, and one end of the capacitor C1 and one end of the switch S2 are connected to the other end of the switch S1. The other end of the capacitor C1 is grounded. The other end of the switch S2 is connected to the inverting terminal of the operational amplifier OA and one end of the capacitor C2. The other end of the capacitor C2 is connected to the output terminal of the operational amplifier OA, and the non-inverting terminal of the operational amplifier OA is grounded. The inverter INV inverts the clock and applies it to the switch S2. For this reason, the switch S1 and the switch S2 are alternately turned on and off by the clock.

When the switch S1 is turned on, the capacitor C1 is charged up to the voltage VIN. The charge amount of the capacitor C1 becomes VIN × C1 in half a clock cycle. When the switch S2 is turned on in the next clock half cycle, the charge of the capacitor C1 is sent to the capacitor C2. Therefore, the amount of charge sent from the voltage VIN to the inverting terminal of the operational amplifier OA in one clock cycle is VIN × C1. The current I is
I = Q / T = VIN × C1 / T = VIN × C1 × fCLK
Is required. T is the clock period.

The equivalent resistance R is
R = VIN / I = 1 / (C1 × fCLK)
It becomes. The equivalent resistance R corresponds to the resistance of an integrator using a resistor, a capacitor, and an operational amplifier. That is, at the time of clock input, the switch S1, the switch S2, and the capacitor C1 operate in the same manner as a resistor and have filter characteristics.

  The switched capacitor notch filter 22 has a first switched capacitor notch filter 22a and a second switched capacitor notch filter 22b, and each filter has an integrator shown in FIG. 4 inside.

  Specifically, the first switched capacitor notch filter 22a is cascaded in eight stages, and the second switched capacitor notch filter 22b is cascaded in eight stages.

  Here, the first switched capacitor notch filter 22a for one stage will be described with reference to FIG. 5, and the second switched capacitor notch filter 22b for one stage will be described with reference to FIG.

  First, the first switched capacitor notch filter 22a for one stage will be described with reference to FIG. FIG. 5 shows the circuit configuration and the frequency characteristics of each part. Of the frequency characteristics, the amplitude characteristics are indicated by solid lines and the phase characteristics are indicated by dotted lines.

  The first switched capacitor notch filter 22a includes resistors R1 to R6, an operational amplifier 31, an adder 32, and integrators 33 and 34.

  In the operational amplifier 31, the non-inverting terminal (+) is grounded, the voltage VIN via the resistor R1 is input to the inverting terminal (−), and one end of the resistor R2, one end of the resistor R3, and one end of the resistor R4 are connected. . The output terminal of the operational amplifier 31 is connected to the other end of the resistor R2 and the adder 32 via the pin P1.

  The adder 32 subtracts a voltage obtained by dividing the voltage fed back from the integrator 34 by the resistors R5 and R6 from the output voltage of the operational amplifier 31 and outputs a subtracted output voltage to the integrator 33.

  The integrator 33 is composed of an integrator composed of a switched capacitor as shown in FIG. 4 and functions as a band-pass filter that allows a predetermined frequency range of the output voltage from the adder 32 to pass through. The other end of R3 and the integrator 34 are output.

  The integrator 34 is composed of an integrator made up of a switched capacitor as shown in FIG. 4 and functions as a low-pass filter that passes the low frequency range of the output voltage from the integrator 33, and the output voltage is connected to the resistor R4. And the other end of the resistor R5.

  According to the first switched capacitor notch filter 22a described above, the operational amplifier 31 subtracts the output voltage of the BPF (bandpass filter) fed back from the integrator 33 from the input voltage VIN, so that the BEF (band elimination filter). Works as. Further, since the operational amplifier 31 subtracts the output voltage of the LPF fed back from the integrator 34 from the input voltage VIN, it operates as an HPF. Therefore, a high-pass notch output having a function of a notch filter and a function of a high-pass filter that greatly attenuates about 7.5 kHz is obtained from the output terminal of the operational amplifier 31.

  Next, the second switched capacitor notch filter 22b will be described with reference to FIG. FIG. 6 shows the circuit configuration and the frequency characteristics of each part. Of the frequency characteristics, the amplitude characteristics are indicated by solid lines and the phase characteristics are indicated by dotted lines.

  The second switched capacitor notch filter 22b includes resistors R7 to R11, RL, RH, and RG, operational amplifiers 41 and 45, an adder 42, and integrators 43 and 44.

  In the operational amplifier 41, the non-inverting terminal (+) is grounded, the voltage VIN through the resistor R7 is input to the inverting terminal (−), and one end of the resistor R8 and one end of the resistor R9 are connected. The output terminal of the operational amplifier 31 is connected to the other end of the resistor R8 and the adder 42 via the pin P1.

  The adder 42 subtracts a voltage obtained by dividing the voltage fed back from the integrator 44 by the resistor R10 and the resistor R11 from the output voltage of the operational amplifier 41, and outputs a subtracted output voltage to the integrator 43.

  The integrator 43 is composed of an integrator composed of a switched capacitor as shown in FIG. 4 and functions as a band-pass filter that allows a predetermined frequency range of the output voltage from the adder 42 to pass. The other end of R9 and the integrator 44 are output.

  The integrator 44 is composed of an integrator composed of a switched capacitor as shown in FIG. 4, and functions as a low-pass filter that passes the low frequency range of the output voltage from the integrator 43, and the output voltage is connected to the resistor R10. And output to one end of the resistor RL.

  The non-inverting terminal of the operational amplifier 45 is grounded, and the other end of the resistor RL, one end of the resistor RH, and one end of the resistor RG are connected to the inverting terminal. The other end of the resistor RH is connected to the output terminal of the operational amplifier 41, and the other end of the resistor RG is connected to the output terminal of the operational amplifier 45.

  From the output terminal of the operational amplifier 45, a low-pass notch output having a function of a low-pass filter and a function of a notch filter that substantially attenuates the vicinity of about 12 kHz is obtained.

  The switched capacitor notch filter 22 synthesizes the high-pass notch output from the operational amplifier 31 shown in FIG. 5 and the low-pass notch output from the operational amplifier 45 shown in FIG. 6 to significantly attenuate about 7.5 kHz to about 12 kHz. Function as. As shown in FIG. 2, about 80 dB can be attenuated at about 7.5 kHz to about 12 kHz.

  Since the modulation frequency 1f is 9.8 kHz, the center frequency is about 7.5 kHz to about 12 kHz, and the modulation frequency 1f can be attenuated by about 80 dB.

  The switched capacitor notch filter 22 is composed of a filter IC that can determine the center frequency based on the clock frequency. The switched capacitor notch filter 22 generates aliasing that is noise seen at twice the clock frequency.

  Therefore, the first LPF 23 is a low-pass filter having a cutoff frequency lower than the aliasing frequency generated by the switched capacitor notch filter 22, and removes aliasing generated by the switched capacitor notch filter 22.

  The lock-in amplifier 18 obtains a 2f signal by performing synchronous detection at twice the frequency of the modulation signal included in the signal from the first LPF 23. It can also be seen from the characteristics of FIG. 2 that the 19.6 kHz signal that is the 2f signal, that is, the synchronous detection signal, is not attenuated.

  The second HPF 24 eliminates low frequency noise and DC components generated by the switched capacitor notch filter 22. The signal analysis circuit 19 calculates the gas concentration based on the second harmonic component from the lock-in amplifier 18.

  As described above, according to the laser type gas analyzer of the first embodiment, the 1f signal is removed by the 16-stage switched capacitor notch filter 22, and the 2f signal is accurately detected by the subsequent-stage lock-in amplifier 18, so that the signal analysis can be performed. Yes.

  Conventionally, an active bandpass filter such as a multiple feedback type secondary bandpass filter shown in FIG. 7 or a twin T-notch filter shown in FIG. 8 is used. Frequency fluctuation of about several hundred Hz and reduction of gain are observed. For this reason, when these active bandpass filters are configured in multiple stages, the filter characteristics change due to individual differences in each stage.

  On the other hand, the switched capacitor notch filter 22 of the present invention does not change the filter characteristics due to temperature changes and tolerances, and has a steep attenuation characteristic. Therefore, only the 1f signal is reduced and the 2f signal is not affected. The switched capacitor notch filter 22 can be realized by determining the cutoff frequency based on the clock frequency and the capacitance of the capacitor. Further, the cutoff frequency can be reduced to ± 1 ppm / ° C. with respect to temperature change.

  Therefore, the filter characteristics do not change due to temperature changes or electronic component tolerances, and a signal having a frequency twice the frequency of the modulation signal can be accurately detected. Thereby, a dynamic range becomes large and the sensitivity in a gas analysis can be improved.

  FIG. 9 is a circuit configuration diagram of the laser gas analyzer according to the second embodiment. FIG. 9 shows a laser gas analyzer according to the second embodiment. FIG. 1 shows the laser gas analyzer according to the first embodiment except that the first HPF 21 is deleted and the switched capacitor notch filter 22 is used. A path filter 26 is provided. The switched capacitor bandpass filter 26 passes only the 2f signal out of the signal from the preamplifier 20.

  FIG. 10 is a diagram illustrating frequency characteristics of the switched capacitor bandpass filter of the laser gas analyzer according to the second embodiment. The switched capacitor bandpass filter 26 passes about 15 kHz to about 25 kHz with the frequency of 19.6 kHz of the 2f signal as the center frequency, and attenuates the frequency of 9.8 kHz of the 1f signal by about 80 dB.

  Next, the switched capacitor bandpass filter 26 will be described with reference to FIG. FIG. 11 shows the circuit configuration and the frequency characteristics of each part. FIG. 11B shows the amplitude characteristic with a solid line and the phase characteristic with a dotted line in the frequency characteristic.

  The switched capacitor bandpass filter 26 is configured by cascaded 16 stages of switched capacitor bandpass filters shown in FIG.

  The switched capacitor bandpass filter 26 includes resistors R20 to R23, an operational amplifier 61, an adder 62, and integrators 63 and 64.

  In the operational amplifier 61, the non-inverting terminal (+) is grounded, the voltage VIN via the resistor R20 is input to the inverting terminal (−), and one end of the resistor R21, one end of the resistor R22, and one end of the resistor R23 are connected. . The output terminal of the operational amplifier 61 is connected to the other end of the resistor R21 and the adder 62 via the pin P11.

  The adder 62 subtracts the ground voltage from the output voltage of the operational amplifier 61 and outputs the subtracted output voltage to the integrator 63.

  The integrator 63 is composed of an integrator composed of a switched capacitor as shown in FIG. 4 and functions as a band-pass filter that allows a predetermined frequency range of the output voltage from the adder 62 to pass. The other end of R22 and the integrator 64 are output.

  The integrator 64 is composed of an integrator made up of a switched capacitor as shown in FIG. 4, and functions as a low-pass filter that passes the low frequency range of the output voltage from the integrator 63, and the output voltage is connected to the resistor R23. Is output at one end.

  According to the above switched capacitor band pass filter 26, the high pass output from the operational amplifier 61, the band pass output from the integrator 63, and the low pass output from the integrator 64 are fed back to the inverting terminal of the operational amplifier 61. Since there is no negative feedback from the integrator 64, it operates as a bandpass filter.

  As described above, the laser gas analyzer of the second embodiment can obtain the same effects as those of the laser gas analyzer of the first embodiment.

DESCRIPTION OF SYMBOLS 10 Laser light source 11 Sine wave generator 12 Saw wave generator 13 Adder 14 Laser drive circuit 15 Sample cell 16 Photo diode 17 Active band pass filter 18 Lock-in amplifier 19 Signal analysis circuit 20 Preamplifier 21 1st high pass filter (1st HPF)
22 switched capacitor notch filter 22a first switched capacitor notch filter 22b second switched capacitor notch filter 23 first low pass filter (first LPF)
24 Second high-pass filter (second HPF)
26 Switched capacitor bandpass filter

Claims (8)

A laser light source for outputting laser light;
A laser driving circuit for driving the laser light source by causing a current in which a high-frequency modulation signal is superimposed on a sweep signal to flow to the laser light source;
A light detection unit that receives laser light from the laser light source through a cell;
A switched capacitor notch filter for removing a fundamental frequency of the modulation signal from an output from the light detection unit;
An extraction unit for extracting the second harmonic signal of the modulation signal by synchronously detecting the output of the switched capacitor notch filter;
A signal analysis circuit for analyzing the second harmonic signal extracted by the extraction unit and measuring the gas concentration;
A laser type gas analyzer characterized by comprising: A laser light source for outputting laser light;
A laser driving circuit for driving the laser light source by causing a current in which a high-frequency modulation signal is superimposed on a sweep signal to flow to the laser light source;
A light detection unit that receives laser light from the laser light source through a cell;
A switched capacitor bandpass filter that passes the second harmonic signal of the modulation signal from the output from the light detection unit;
An extractor for extracting a second harmonic signal of the modulated signal by synchronously detecting the output of the switched capacitor bandpass filter;
A signal analysis circuit for analyzing the second harmonic signal extracted by the extraction unit and measuring the gas concentration;
A laser type gas analyzer characterized by comprising:   The laser gas analyzer according to claim 1, further comprising a first high-pass filter that removes the sweep signal from an output from the light detection unit on an input side of the switched capacitor notch filter.   4. The low-pass filter for removing aliasing noise generated at a frequency twice the clock frequency used in the switched capacitor notch filter is provided on the output side of the switched capacitor notch filter. The laser type gas analyzer as described.   The low-pass filter for removing aliasing noise generated at a frequency twice as high as a clock frequency used in the switched-capacitor band-pass filter is provided on the output side of the switched-capacitor band-pass filter. Laser gas analyzer. The switched capacitor notch filter is
An inverting terminal is connected to one end of the input resistor, one end of the second resistor, one end of the third resistor, and one end of the fourth resistor, and an output terminal is connected to the other end of the second resistor. One op amp,
A first adder connected to an output terminal of the first operational amplifier;
A switched capacitor having a first switch, a second switch, a first capacitor, a second capacitor, and a second operational amplifier is connected to the other end of the third resistor, and the output of the first adder is input. A first integrator,
A switched capacitor having a third switch, a fourth switch, a third capacitor, a fourth capacitor, and a third operational amplifier is connected to the other end of the fourth resistor, and the output of the first integrator is input. A second integrator,
5. The laser type gas analyzer according to claim 1, wherein the first adder subtracts an output of the second integrator from an output of the first operational amplifier. 6. The switched capacitor notch filter is
A fourth operational amplifier in which an inverting terminal is connected to one end of the sixth resistor and one end of the seventh resistor, and an output terminal is connected to the other end of the sixth resistor;
A second adder connected to the output terminal of the fourth operational amplifier;
A switched capacitor having a fifth switch, a sixth switch, a fifth capacitor, a sixth capacitor, and a fifth operational amplifier is connected to the other end of the seventh resistor, and the output of the second adder is input. A third integrator,
A fourth integrator comprising a switched capacitor having a seventh switch, an eighth switch, a seventh capacitor, an eighth capacitor, and a sixth operational amplifier, to which the output of the third integrator is input;
An inverting terminal is connected to an output terminal of the fourth integrator through an eighth resistor, an output terminal of the fourth operational amplifier through a ninth resistor, and one end of the tenth resistor, and an output terminal of the tenth resistor is connected. A seventh operational amplifier connected to the other end;
The laser gas analyzer according to claim 6, wherein the second adder subtracts the output of the fourth integrator from the output of the fourth operational amplifier. The switched capacitor bandpass filter is
An inverting terminal is connected to one end of the input resistor, one end of the second resistor, one end of the third resistor, and one end of the fourth resistor, and an output terminal is connected to the other end of the second resistor. One op amp,
An adder for subtracting a predetermined voltage from the output of the first operational amplifier;
A switched capacitor having a first switch, a second switch, a first capacitor, a second capacitor, and a second operational amplifier is connected to the other end of the third resistor, and an output of the adder is input. One integrator,
A switched capacitor having a third switch, a fourth switch, a third capacitor, a fourth capacitor, and a third operational amplifier is connected to the other end of the fourth resistor, and the output of the first integrator is input. A second integrator,
The laser gas analyzer according to claim 2 or 5, wherein

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